Extensor Pollicis Brevis

Posterior Interosseus, Radial Nerve, Posterior Cord, Posterior Division, Middle and Lower Trunk, C7, C8. 

Dorsal surface of radial shaft below abductor pollicis longus and in the interosseus membrane. 

Insert needle electrode directly over the ulnar side of radius, four fingerbreadths proximal to wrist. The electrode will travel through the extensor digitorum communis. 

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Fig. 10.11 a—c. Extensor tendons first compartment, a Short-axis 15-7 MHz US image obtained over the first compartment of the extensor tendons with b diagram correlation demonstrates the abductor poUicis longus (APL) and extensor pollicis brevis (EPB) tendons which appear closely apposed and retained over the radial styloid by the retinaculum (arrowheads). The radial artery (RA) is seen on the lateral aspect of the abductor pollicis longus. c Probe positioning and field-of-view of the US image relative to the dorsal wrist structures... 

Kg.l0.13a,h. Radial artery. Transverse 15-7 MHz US images obtained a at the radial styloid and, more distally, b at the scaphoid bone level demonstrate the relationship of the radial artery (a) and veins (v) with the abductor poUicis longus (APL) and the extensor pollicis brevis (EPB) tendons. As the radial vessels proceed distally, they pass deep to the extensor tendons crossing the floor of the anatomic snuff-box to reach the dorsal aqtect of the hand. The inserts at the upper sides of the figure indicate prohe positioning... 

Fig. 10.14a-d. Radial nerve, a Photograph of the lateral aspect of the wrist showing the relationship of the superficial cutaneous branch of the radial nerve (white dashed line) with the extensor tendons of the first (I) and third (111) compartment, b-d Transverse 15-7 MHzUS images over the first compartment of the extensor tendons obtained at the levels (horizontal black bars) indicated in a show the radial nerve (arrow) as it crosses the abductor pollicis longus (APL) and extensor pollicis brevis tendons (EPB) to reach the dorsal aspect of the hand. At the wrist, the radial nerve is very small and can be depicted as a tiny hypoechoic image only when very high-frequency transducers are used... 

Fig. 10.38 a-c. Wartenberg syndrome. a,b Short-axis and c long-axis 15-7 MHz US images over the radial nerve at the wrist in a patient with symptoms of superficial radial neuropathy after intravenous infusion in the cephalic vein, a Proximal to the level of injury, a normal-appearing nerve (arrow) is seen adjacent to an occluded cephalic vein (arrowhead). b,c At the level of puncture, a fusiform hypoechoic thickening of the nerve (arrow) with loss of the fascicular echotexture can be appreciated as a result of trauma. Note the position of the nerve relative to the abductor pollicis longus (APL) and extensor pollicis brevis (EPB) tendons... 

If the electrode is inserted too proximally it will be in the extensor carpi radialis brevis if inserted too distally it will be in the extensor pollicis brevis if it is inserted too ulnarly or too superficial, it will be in the extensor digitorum communis. 

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